Studies are proposed to continue our research in the following areas: 1. The effect of starvation, various nutrients, fetal and neonatal life, hypothyroidism and the sex steroids on the in vitro metabolism of the thyroid function in the rat. Further studies in fasted man on the absorbtion of T4 and the effect of specific nutrients on TH metabolism and on the LH and FSH responses to LH-RH are proposed. 2. The metabolic activity of reverse T3 (rT3). 3. The use of the rat epididymal fat pad (EFP) as a marker of the peripheral activity of growth hormone (GH) and the interaction of TH in this system. 4. The physiologic role of thyrotropin releasing hormone (TRH) in the fetal and neonatal development of the pituitary-thyroid axis in the rat and regulation of TRH secretion as assessed in the peripheral blood of the young rat which lacks serum TRH degrading enzymes. Further studies on the effect of acute doses of dilantin on the hypothalamic-pituitary-thyroid troica in rat and man. 6. The peripheral metabolism of innter ring 125 I-labeled T3 and T2. 7. A series of studies of the effect of pharmacologic quantities of iodide on fetal, neonatal and adult thyroid function in the rat, on the possible induction of chronic thyroiditis in rats and mice with other auto-immune disorders and on thyroid function in diabetic patients receiving the sulfonylureas. The effect of chronic physiologic quantities of iodide on thyroid function in euthyroid patients with Hashimoto's thyroiditis and normal subjects will be evaluated.